Rex is a friendly dinosaur toy; he also scares very easily. Rex wants nothing more than to impress his friends when he can, which often happens by accident. He enjoys playing video games such as Verum Rex and his favorite character is Yozora. However, Rex shows very little common sense, as he mistakes Sora, Donald, and Goofy for characters from the game due to their similar attire, when there are obvious differences.

Rex first appeared in 1995, in Pixar's first feature film Toy Story, voiced by Wallace Shawn. In the film, he is depicted as rather close to Woody and chooses not to take sides in the ensuing conflict between Woody and Buzz, especially when Woody accidentally knocks Buzz out of the window. In Toy Story 2, released in 1999, Rex is shown to be a fan of video games as he is shown playing a Buzz Lightyear game in the film's opening, later finding the game's strategy guide at Al's Toy Barn while trying to find Woody who had since been kidnapped by Al himself.